This invention relates to the field of heat transfer to a moving fluid and the optimization of this transfer in the presence of nucleate boiling.
The relatively large quantities of heat transfer achievable through use of the heat of vaporization of liquids is attractive for cooling electronic parts as well as for other heat transfer purposes. The use of this heat transfer mechanism in the steam heating of buildings and for industrial purposes is a common example of the large and effective application of this heat transfer mechanism in everyday life. The boiling portion of this heat transfer mechanism is found, however, to be attended by certain heat transfer difficulties or disadvantages, especially when the shapes, sizes, flow rates, materials, and nucleate boiling that are desirable for cooling electronic parts are considered.
More precisely, when an electronic part such as an integrated circuit chip protrudes into the stream of a cooling fluid, it is found that the occurrence of nucleate boiling at the leading edge of the electronic part can result in a secondary effect decrease in overall heat transfer effectiveness and some attending difficulties. When the vapor formed by leading edge boiling at the cooled electronic part is carried over the larger and most effective heat transfer surface of the electronic part, i.e., when this vapor is carried over the top area surface of the part a decrease in cooling effectiveness is found to occur. In this condition, the large surface area of the part is in fact partially shielded from liquid contact by the flow carried vapor which intervenes between the fluid body and the surface area of the electronic part.
In the present invention, the occurrence of this problem is recognized and is addressed with a class of solutions that are easily added to the electronic part environment in a cost-effective manner.
The U.S. patent art has recognized the desirability of efficient heat transfer through a moving fluid in several patents which are of general background interest with regard to the present invention. Included in this art is U.S. Pat. No. 5,158,136 issued to K. Azar and concerned with a pin fin heat sink which includes a flow enhancement improvement. In the Azar invention flow guide members are added around a pin fin heat sink and a gap is provided between the lower edges of the flow guide members and a base surface of the heat sink in order that potentially stagnant fluid in an interior region of the pin fin field be allowed to communicate with fluid flowing around the exterior of the heat sink. This arrangement enables a so-called "pumping" action in which the potentially stagnant fluid is drawn along with fluid flowing around the exterior of the heat sink. Since the Azar invention is concerned with a pin fin heat sink structure and with stagnant flow reduction and discloses only minimal or no nucleate boiling, the present invention is readily distinguished from the disclosure of the Azar patent.
The U.S. Pat. No. 5,077,601 of T. Hatada et al is also of this general background interest with respect to the present invention. The Hatada et al patent is concerned with a cooling system for an electronic device and a heat radiating fin for use in the cooling system. In the Hatada invention a cooling fluid, preferably air, is provided with a greater cross-sectional area at an upstream end of the electronic device with the cross-sectional area progressively decreasing toward the downstream end of the device's flow passage. The Hatada invention employs a number of obliquely disposed and airflow conforming heat exchange elements in the tinned assembly. Since the Hatada invention is not concerned with boiling or with the limitation of boiling degradation of a heat exchange arrangement, a ready distinction between the present invention and the Hatada et al apparatus is apparent.
U.S. Pat. No. 4,999,741 issued to S. G. Tyler is also of general interest with respect to the present invention and is concerned with a thermally conducting flexible membrane which may be disposed in intimate and heat conducting relationship with an electronic device in order to both hermetically seal the device and provide large area thermal contact with the device. Since the Tyler patent is also not concerned with boiling of a liquid coolant, a ready distinction with the present invention is apparent.